1. Field of the Invention
The present invention relates to a method and apparatus for the measurement of three-dimensional surface coordinates of an object with controlled movement along a slit line. More particularly the present invention provides an improved method of computing the coordinates of a line-scan based object.
2. Description of the Prior Art
The prior art has several examples of devices that utilize a light stripe and image sensors to obtain the coordinates of a subject object. The conventional triangulation computation is a cost effective method. Several references disclose methodologies using triangulation to compute the coordinates of an object. The triangulation methods become cost effective and highly precise when implemented with a PC. One example of such a prior art reference is the “Method and Apparatus for Measuring Profile of Three-Dimensional Object”, of Yukio Sato et al, U.S. Pat. No. 4,794,262, issued Dec. 27, 1988. Another is the “XYZ Coordinates Measuring System” of Osamu Ozeki, Kazunori Higuchi, and Shin Yamamoto, U.S. Pat. No. 4,961,155, issued Oct. 2, 1990. Still another triangulation based method is described in “A Simple Method for Range Finding Via Laser Triangulation”, by Hoa G. Nguyen and Michael R. Blackburn, published in January, 1995, as NraD technical document 2734. An example of a current art product utilizing a triangulation method is the IVP Ranger SAH5, by IVP Integrated Products, Inc.
In conventional triangulation methods, the use of the focus length of the image sensor must be used in the computation of the position of the subject object. Since the focus length is small relative to the distance from the sensor to the object, the measured value of the focus length significantly affects the accuracy of the computation.
Accordingly, it is an object of the present invention to provide a computation method which is independent of the focus length, thereby improving the accuracy of the position computation.
It is another object of the present invention to provide a new technique to improve the surface scan capability on various objects. A light source and an image sensor (collectively referred to as a scan module) are used in conventional triangulation-based methods. However, the current art devices available on the market are limited, typically in one of two ways: (1) The scan module itself is typically a stand alone item, such as the LD100*-*F and the LD250*-*F Laser Distance Meters manufactured by the Toshiba Corporation, and the device disclosed in “A Laser Range Scanner Designed for Minimum Calibration Complexity”, by James Davis and Xing Chen in the 2001 IEEE Proceedings of the 3rd International Conference on Digital Imaging and Modeling. (2) Multiple scan modules are utilized, but each scan module operates independently of the others. Devices employing this scheme are exemplified by the KLS 51 and KLS 171 Laser Sensors from Kreon Technologies. The present invention employs multiple scan modules aligned together to jointly scan the object and produce the combined line based coordinates. Using this arrangement, more accurate measurement results and reduced occlusion can be achieved.